Raiatea Fruit-dove (Ptilinopus chrysogaster) is found only in the Leeward Islands (Society Islands), French Polynesia, where it is restricted to the islands of Raiatea, Tahaa, Huahine, Bora Bora and Maupiti. The species is poorly known, but on Raiatea at least it is thought to occur up to 450 m in forest (Gibbs et al. 2001).
In 1973 the populations on Tahaa, Bora Bora and Maupiti were estimated to be 500, 50 and 100 individuals respectively (Gibbs et al. 2001), while the species is considered relatively common on Raiatea and Huahine. Therefore, the overall population size has been assessed as falling in the range 1,000-2,499 mature individuals. The population is currently considered stable in the absence of evidence for declines or severe threats (see BirdLife International 2017), though there may be limited hunting of the species in parts of its range and the invasive Swamp Harrier (Circus approximans) may have had an effect on the species at least in the past (del Hoyo et al. 1997, Gibbs et al. 2001). Thus, given the species’ small population size and its restricted range the species has been listed as Near Threatened under criteria D1+2.
The recent regional Red List for France, including French Polynesia (UICN France et al. 2015) listed this species as Endangered under criterion B2ab(iii,v). The criteria string suggests that the species was assessed as declining, contrary to the current global listing, and so the species’ status likely requires another examination. At the very least, though, the assessment by UICN France et al. (2015) did not provide a full assessment for the species, as its Extent of Occurrence falls below the threshold for Endangered too, and so if it is listed under B2 it should also be listed under B1. Therefore, the species has been reassessed here under all criteria.
Criterion A – The species is currently assessed as ‘stable in the absence of evidence for any declines or substantial threats’ (BirdLife International 2017). In the UICN France et al. (2015) assessment the sub-conditions of the criteria string imply that the species had been assessed as declining. However, there was no further evidence for why the species was considered to be declining. Even if it were accepted that the species is in decline, there still remains a lack of any quantification of the rate of decline and so the species cannot be assessed against this criterion.
Criterion B – This species has an Extent of Occurrence (EOO) of 3,800km2, meeting the threshold for Endangered under criterion B1. The species’ Area of Occupancy (AOO) has not been calculated to IUCN guidelines (IUCN Standards and Petitions Subcommittee 2017), though if the known area of each island is used as a rough estimate (in total c.373km2) then the species would meet the threshold for Endangered under criterion B2 also.
To warrant listing under criteria B1 and B2, though, at least two further conditions must be met. It is unlikely that the species is severely fragmented, but the species does only occur on five small islands. The important question is then whether these five islands each individually qualify as a ‘location’ by IUCN definitions (see IUCN Standards and Petitions Subcommittee). When calculating the number of ‘locations’, it is important to know the area of impact of the most important threat. The lack of any supporting information in the UICN France et al. (2015) document therefore hinders an assessment of the number of locations where this species is found. For example, if we now have clear evidence for a current population decline due to Swamp Harriers (rather than only for past declines) then it is likely that each island would be a ‘location’. However, if the new information forming the basis of the decline in UICN France et al. (2015) is low level habitat loss then the number of locations will likely be >10. Thus information is needed to ascertain what the main threat behind the proposed decline is.
Information about the potential threats is also sought to identify whether the species should actually be assessed as declining in the context of this criterion. For a species to be listed as declining in the context of criteria B and C, a species must be undergoing a continuing decline (i.e. a one-off reduction would not count) and the information required to support this needs to be at least ‘inferred’ (see IUCN Standards and Petitions Subcommittee 2017). Thus ‘suspected’ declines cannot be used.
The situation here is made more complicated by the current listing stating that the Swamp Harrier had an effect on the species in the past. As the Harrier is considered to have impacted the species in the past it may be appropriate to infer that its continued presence within the species’ range is causing a continuing decline. However, further information regarding this is required before the population trend can be altered.
If this information is accepted then the species would warrant listing as Endangered under criteria B1ab(v)+2ab(v). This, however, still leaves a discrepancy with UICN France et al. (2015) regarding condition b(iii), which refers to a continuing decline in the area/extent/quality of habitat. Further information is thus sought regarding whether there is any such decline in habitat to see whether the species would also meet this condition. Note, though that if a decline in habitat is the only reason for the considered decline in population then the number of locations would no longer meet the required threshold and the species would not warrant listing as threatened under criterion B at all.
Criterion C – Whether the species is listed under this criterion depends again on information regarding the population trend. The population size range of 1,000-2,499 mature individuals meets the threshold value for Endangered, but given that the species is found in multiple subpopulations and is not known to undergo extreme fluctuations it doesn’t meet the conditions for listing under C2a(ii) or C2b. The 1973 population figures do suggest that at least one subpopulation contains >250 mature individuals, though minimum estimates would place no subpopulation as having >1,000 mature individuals. Therefore, unless there are any new population size figures available the species would not warrant listing as Endangered under criterion C2a(i), instead warranting listing as Vulnerable, but that is as long as there is evidence for a continuing decline. If the evidence is actually more circumstantial and as such of a lower confidence level, the species may instead warrant listing as Near Threatened under criterion C2a(i); but if there is no clear evidence for a decline then the species would not warrant listing under this criterion. Therefore, more information regarding any potential population decline is required.
Criterion D – The information currently held for this species has not changed given the new information from UICN France et al. (2015). The population size still approaches the threshold for Vulnerable under criterion D1, and while the species is found only on five small islands no future threat is present that is likely to drive the species Extinct or Critically Endangered in a very short period of time (one or two generations [3.2 or 6.4 years]) (see IUCN Standards and Petitions Subcommittee 2017). Therefore, the species warrants listing as Near Threatened under criteria D1+2.
Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been carried out for this species. Therefore, it cannot be assessed against this criterion.
Overall, for a clear reassessment further information is urgently needed, particularly regarding the population trend and the justification for this trend. Without any clear information regarding this it is unlikely that the species could be properly reassessed, and the species could remain as Near Threatened. If there is good, clear information available though, the species could warrant uplisting to Vulnerable or Endangered.
We welcome any comments regarding this, but please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in this topic.
BirdLife International. 2017. Species factsheet: Ptilinopus chrysogaster. Downloaded from http://www.birdlife.org on 23/11/2017.
del Hoyo, J.; Elliott, A.; Sargatal, J. 1997. Handbook of the birds of the world, Vol 4: Sandgrouse to Cuckoos. Barcelona, Spain: Lynx Edicions.
Gibbs, D.; Barnes, E.; Cox, J. 2001. Pigeons and doves: a guide to the pigeons and doves of the world. Pica Press, Robertsbridge, U.K.
IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.
UICN France; MNHN; SOP Manu. 2015. La Liste rouge des espèces menacées en France – Chapitre Oiseaux de Polynésie française. Paris, France.